1. Field of Invention
The present invention relates generally to the field of wireless communication and data networks. More particularly, in one exemplary aspect, the present invention is directed to wireless communications system using multiple air interfaces and multiple antennas, including a multiple-in, multiple-out (MIMO) antenna.
2. Description of Related Technology
Wireless connectivity is becoming ubiquitously available and necessary in computing and entertainment products. Presently, many telecommunications products such as mobile phones, computers, media players, etc. come equipped with one or more wireless networking or communication interfaces.
In many cases, these network interfaces may include both wired and wireless network interfaces. Wireless network interfaces, also called “air interfaces”, are of increasing interest due to the mobility and freedom they afford a user. Exemplary wireless networking technologies include WiFi (IEEE Std. 802.11a/b/g/n), WiMAX (IEEE Std. 802.16), PAN (IEEE Std. 802.15), IrDA, ultra wide band (UWB), Mobile Wideband (MWBA; IEEE-Std. 802.20), and others.
To increase the transmission bitrates of a wireless system, use of multiple antennae for transmission/reception has gained popularity. Such systems are called multiple-in, multiple-out systems (MIMO) and may employ multiple transmitting or multiple receiving antennae or both. See, e.g., IEEE-Std. 802.11n, which employs a MIMO approach in the context of a WLAN environment, as well as IEEE-Std. 802.16e (WiMAX), each of the foregoing being incorporated herein by reference in its entirety.
As a result of the growth in the total number of antennae used in communication, both due to multiple air interfaces and due to MIMO antenna systems, designers of hardware platforms are faced with a challenging task of optimal antenna placement. The problem is exacerbated when the form factor of a hardware platform is small or otherwise dimensionally or spatially constrained, thus giving a designer less flexibility in placing antennae on the hardware platform. Moreover, other factors which can affect antenna isolation and/or placement, including the use of a metallic housing or case for the device, present additional challenges.
Furthermore, since several radios have to support multiple bands, such as WLAN and WiMAX, the antenna size typically cannot be compromised to achieve acceptable performance.
Additionally, since certain isolation is required in order to obtain acceptable MIMO performance, extra burden is added to the design process in order to separate the antennas sufficiently to provide such isolation, even if these antennas are for the same radio.
One salient reason why antenna placement is of critical importance relates to the potential electromagnetic interference between two (or more) antennae. This interference may occur because these two antennae may be carrying communication data over two different air interfaces on a hardware platform, and may be using the same portion of the radio frequency spectrum (or spectrum portions close enough to create interference). For example, Bluetooth and IEEE-Std. 802.11n devices both operate in the 2.4-2.8 GHz Industrial-Scientific-Medical (ISM) band, and could potentially cause radio interference with one another. Similarly, WiMAX supports 2.3 GHz and 2.5 GHz bands; since WiMAX utilizes a comparatively high transmitter power, it can degrade Bluetooth performance significantly if the antenna isolation is not sufficiently high.
The degree of isolation between potentially interfering antennae impacts the severity of the interference problem. Isolation is generally a function of path loss, or attenuation, suffered by radio frequency (RF) signals from one antenna to the other. If the isolation between antennae of one air interface and antennae of another air interface is sufficiently large, then the interference with one another may be negligible. What is “sufficiently large” isolation may be implementation specific, and may depend on several factors such as receiver sensitivity.
In cases where the isolation is sufficiently large (e.g., >35 db between the first and second air interface antennae), solutions such as the adaptive frequency hopping (AFH) feature of Bluetooth can be employed to provide largely unencumbered simultaneous operation of the two interfaces (e.g., Bluetooth and WLAN).
However, when the isolation between an antenna pair is not sufficiently large (e.g., when the isolation from both antennas from one radio is not sufficiently large with respect to the other radio, such as for WLAN and Bluetooth coexistence cases where both WLAN antennas have less than 30 dB isolation with Bluetooth antenna), the multiple air interfaces may significantly interfere with each other's transmission. It is clearly desirable to mitigate such interference so as to avoid adverse effects on user experience (e.g., Bluetooth audio drop-outs during A2DP streaming playback, slow WLAN and Bluetooth transfer speeds, WLAN link drops, poor Bluetooth mouse tracking, streaming video jitter, etc.). One simple solution in prior art is to time-share or time-division multiplex the use of potentially interfering interfaces—that is, turn off one interface while the other interface is actively transmitting or receiving. However, this solution suffers from the drawback that it may result in an annoying and unsatisfactory user experience, wherein data connectivity on one interface may be broken or intermittent due to activity on the other air interface. For example, speech on a Bluetooth interface may come across segmented or choppy if the interface has to time-division multiplex with a WLAN air interface that is carrying data or voice communication on its air interface.
Other solutions have been proposed as well, including using antenna isolation for selecting transmit and receive antennas. For example, U.S. Pat. No. 6,774,864 to Evans, et al, entitled “Method of operating a wireless communications system,” issued Aug. 10, 2004 discloses a method of selecting a combination of transmit antennas and receive antennas in a MIMO antenna system to give the best isolation from adjacent parallel signal streams comprises transmitting a first signal from one of the transmit antennas and measuring a quality metric, for example signal strength of the received signal at each of the receive antennas. The process is repeated using signals transmitted in turn by each the remaining transmit antennas. A channel matrix is compiled of the transmit antennas versus the receive antennas and a selection is made of a combination of transmit and receive antennas receiving acceptably a first signal and unacceptably a second signal and vice versa. The selected combination is used to send and receive MIMO signals. Switches are provided for coupling the selected antennas to the respective transmitters and receivers.
U.S. Pat. No. 7,366,244 to Gebara, et al. issued Apr. 29, 2008, and entitled “Method and system for antenna interference cancellation” discloses a wireless communication system which can comprise two or more antennas that interfere with one another via free space coupling, surface wave crosstalk, dielectric leakage, or other interference effect. The interference effect can produce an interference signal on one of the antennas. A cancellation device can suppress antenna interference by generating an estimate of the interference signal and subtracting the estimate from the interference signal. The cancellation device can generate the estimate based on sampling signals on an antenna that generates the interference or on an antenna that receives the interference. The cancellation device can comprise a model of the crosstalk effect. Transmitting test signals on the communication system can define or refine the model.
U.S. Pat. No. 7,362,275 to Tu, et al. issued Apr. 22, 2008 and entitled “Internal antenna and mother board architecture” discloses various embodiments of an internal antenna and motherboard architecture. In one embodiment, a wireless device may include a housing enclosing a first motherboard and a second motherboard. The ground plane of the first motherboard may be coupled to the ground plane of the second motherboard within the housing. The first motherboard and the second motherboard may act as an internal antenna system for the wireless device.
U.S. Pat. No. 7,359,730 to Dennis, et al, issued Apr. 15, 2008 and entitled “Method and apparatus for reducing interference associated with wireless communication” discloses a method and apparatus for reducing interference associated with wireless communication in an area having sensitive electronic equipment. A wireless communications device receives, from an access point, a signal having a signal strength above a predetermined threshold. The wireless communications device determines a transmission power level maximum based on the received signal and then transmits a signal to the access point at a transmission power level at or below the transmission power level maximum. The wireless communications device disables the transmission when the signal strength falls below the predetermined threshold.
U.S. Pat. No. 7,352,332 to Betts-LaCroix, et al. issued Apr. 1, 2008 and entitled “Multiple disparate wireless units sharing of antennas” discloses, in one embodiment, an apparatus including, but is not limited to, a first wireless communication unit of a first wireless communication standard, where the first standard includes selecting one of two antennas provided. The apparatus further includes a second wireless communication unit of a second wireless communication standard, where a first antenna and a second antenna are shared by the first and second communication units. Other methods and apparatuses are also described.
U.S. Pat. No. 7,295,860 to Suwa issued Nov. 13, 2007 and entitled “Radio communication apparatus” discloses a radio communication apparatus which comprises a radio unit capable of transmitting or receiving a first radio communication signal of a Bluetooth standard and a second radio communication signal of a cordless phone standard and a synchronism discriminator for discriminating a radio communication standard signal. The radio communication apparatus switches between first and second radio communication modes in response to a discrimination result of the synchronism discriminator, detects a type and a weight of a sound error every mode, and adds or subtracts the weight of the sound error in a present slot to or from a weight of a sound error in the previous slot in response to a degree of the sound error in the present slot. This structure allows a single apparatus to transmit or receive both of two kinds of radio communication standard signals, and the sound error is adequately and precisely handled in response to the type and weight of the sound error, thereby improving quality of the sound signal cancellation.
U.S. Pat. No. 7,253,783 to Chiang, et al. issued Aug. 7, 2007 and entitled “Low cost multiple pattern antenna for use with multiple receiver systems” discloses an antenna assembly including at least two active or main radiating omni-directional antenna elements arranged with at least one beam control or passive antenna element used as a reflector. The beam control antenna element(s) may have multiple reactance elements that can electrically terminate it to adjust the input or output beam pattern(s) produced by the combination of the active antenna elements and the beam control antenna element(s). More specifically, the beam control antenna element(s) may be coupled to different terminating reactances to change beam characteristics, such as the directivity and angular beamwidth. Processing may be employed to select which teiiuinating reactance to use. Consequently, the radiator pattern of the antenna can be more easily directed towards a specific target receiver/transmitter, reduce signal-to-noise interference levels, and/or increase gain. A Multiple-Input, Multiple-Output (MIMO) processing technique may be employed to operate the antenna assembly with simultaneous beam patterns.
U.S. Pat. No. 7,142,864 to Laroia, et al. issued Nov. 28, 2006 and entitled “Methods and apparatus of enhancing performance in wireless communication systems” discloses methods and apparatus for supporting and using multiple communications channels corresponding to different transmit technologies and/or access technologies in parallel within a cell of a wireless communications system. Mobile nodes support multiple technologies and can switch between the technology being used at a particular point in time, e.g., from a first channel corresponding to a first technology to a second channel corresponding to a different technology which provides better transmission characteristics, e.g., a better perceived channel quality. Mobiles maintain at least two sets of channel quality information at any one point in time. Mobiles select the better channel and communicate the channel selection to the base station or communicate channel quality information for multiple channels to the basestation and allow the base station to select the channel corresponding to the technology providing the better conditions for the mobile. Different mobiles in the same cell may support different technologies.
United States Patent Publication No. 20080095263 to Xu et al. published Apr. 24, 2008 entitled “Method And Apparatus For Selection Mechanism Between OFDM-MIMO And LFDM-SIMO” discloses systems and methodologies that facilitate switching between various combinations of MIMO, SIMO, SISO and OFDM, LFDM and IFDM. According to various aspects, a method for a wireless communication network is provided that includes: receiving a first set of data information, wherein the first set of information comprising a first value, determining if the first value is above a threshold and transmitting an indication to switch to using a first transmission technique if determined that the first value is above the threshold.
United States Patent Publication No. 20070238483 to Boirequ et. al published Oct. 11, 2007 entitled “Antenna sharing techniques” discloses a mobile computing device may comprise an antenna, a switch to couple to the antenna, and multiple transceivers to couple to the switch. The mobile computing device may also comprise an antenna management module to couple to the switch and the transceivers. The antenna management module may control the switch to electrically connect one of the transceivers to the antenna. Other embodiments may be described and claimed.
United States Patent Publication No. 20070076649 to Lin et. al published Apr. 5, 2007 entitled “Techniques for heterogeneous radio cooperation” discloses a cooperative communications manager module which establishes a first wireless link with a client device using a first channel frequency and dispatches a first message to the client device over the first channel frequency. The cooperative communications manager module establishes a second wireless link with a destination node and controls the cooperative transmission of the first message simultaneously with the client device to the destination node over the second wireless link using a second channel frequency.
United States Patent Publication No. 20060223450 published Oct. 5, 2006 to Dacosta et al. entitled “Method and apparatus to resist fading in MIMO and SIMO wireless systems” discloses a wireless communication system, the receiver includes a first plurality of receive chains and a second plurality of antennas. Each receive chain is selectively connectable to selected antennas. The antennas are selected based on criteria obtained from a received RF signal to produce an antenna configuration connected to the receive chains to reduce RF fading at the receiver. An electronic switch connects the antennas to the receive chains. The receiver is programmed to determine which antenna should be connected to each receive chain by the switch by measuring characteristics of the received signal for each allowed antenna configuration and selecting the best antenna configuration. Transmitters may be similarly configured.
United States Patent Publication No. 20060034217 published Feb. 16, 2006 to Kwon et al. entitled “Method and network device for enabling MIMO station and SISO station to coexist in wireless network without data collision” discloses a method of enabling a multi-input multi-output (MIMO) station and a single input single output (SISO) station to coexist in a wireless network and a wireless network device. The method includes receiving information on a station when the station accesses a wireless network, setting coexistence information by comparing a number of antennas of the station accessing the wireless network with a number of antennas of a plurality of stations constituting the wireless network, and transmitting a frame containing the coexistence information to the plurality of stations constituting the wireless network.
Despite the foregoing variety of approaches to MIMO and multiple air interface co-existence, there is a need for an improved method and apparatus for mitigating potential interference between antennae of different air interfaces on the same hardware platform. Specifically, a salient need exists for a solution which addresses platforms that are highly space-constrained or otherwise necessarily result in low isolation values between the antennae of the various air interfaces of the platform (for example, WiFi/WLAN and Bluetooth, WiMAX and Bluetooth, WLAN and UWB). Such an improved solution would ideally permit for good user experience (i.e., devoid of any significant audio or data drop-outs, effects on data streaming rate, preclusion of use of one interface when another is being used, and so forth which would adversely affect user satisfaction) and be absent significant operation restrictions with respect to the multiple air interfaces (e.g., allow two or more interfaces to operate simultaneously in at least partial capacity), while still obeying the platform or form-factor limitations such as those present in extremely small hand-held or laptop computing devices, or those with metallic cases which inherently present challenges to antenna placement.